29-Issue 6

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https://diglib.eg.org/handle/10.2312/157

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A Copula-Based BRDF Model
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Oeztuerk, Aydin; Kurt, Murat; Bilgili, Ahmet
In this paper, we introduce a novel approach for modeling surface reflection. We focus on using a family of probability distributions called Archimedean copulas as BRDF models. The Archimedean representation has an attractive property in that the multivariate distributions are characterized by their marginal distributions through a single univariate function only. It is shown that the proposed model meets the reciprocity property of reflection. Based on measured BRDF data, we demonstrate that the proposed approach provides a good approximation to BRDF. Empirical comparisons are made with some classically used BRDF models.
Computational Aesthetics 2010 in London, England, June 14-15, 2010, sponsored by Eurographics, in collaboration with ACM SIGGRAPH
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Isenberg, Tobias; Dodgson, Neil
Letters to the Editors
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Peters, Ph.D, Thomas J.
Resampling Strategies for Deforming MLS Surfaces
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Gois, Joao Paulo; Buscaglia, Gustavo C.
Moving-least-squares (MLS) surfaces undergoing large deformations need periodic regeneration of the point set (point-set resampling) so as to keep the point-set density quasi-uniform. Previous work by the authors dealt with algebraic MLS surfaces, and proposed a resampling strategy based on defining the new points at the intersections of the MLS surface with a suitable set of rays. That strategy has very low memory requirements and is easy to parallelize. In this article new resampling strategies with reduced CPU-time cost are explored. The basic idea is to choose as set of rays the lines of a regular, Cartesian grid, and to fully exploit this grid: as data structure for search queries, as spatial structure for traversing the surface in a continuation-like algorithm, and also as approximation grid for an interpolated version of the MLS surface. It is shown that in this way a very simple and compact resampling technique is obtained, which cuts the resampling cost by half with affordable memory requirements.
New EUROGRAPHICS Fellows
(The Eurographics Association and Blackwell Publishing Ltd, 2010)
Guest Editorial
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Joan-Arinyo, Robert; Pereira, Joao Madeiras
Application of Visual Analytics for Thermal State Management in Large Data Centres
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Hao, M. C.; Sharma, R. K.; Keim, D. A.; Dayal, U.; Patel, C.; Vennelakanti, R.
Today s large data centres are the computational hubs of the next generation of IT services. With the advent of dynamic smart cooling and rack level sensing, the need for visual data exploration is growing. If administrators know the rack level thermal state changes and catch problems in real time, energy consumption can be greatly reduced. In this paper, we apply a cell-based spatio-temporal overall view with high-resolution time series to simultaneously analyze complex thermal state changes over time across hundreds of racks. We employ cell-based visualization techniques for trouble shooting and abnormal state detection. These techniques are based on the detection of sensor temperature relations and events to help identify the root causes of problems. In order to optimize the data centre cooling system performance, we derive new non-overlapped scatter plots to visualize the correlations between the temperatures and chiller utilization. All these techniques have been used successfully to monitor various time-critical thermal states in real-world large-scale production data centres and to derive cooling policies. We are starting to embed these visualization techniques into a handheld device to add mobile monitoring capability.
Hierarchical Structure Recovery of Point-Sampled Surfaces
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Attene, Marco; Patane, Giuseppe
We focus on the class of regular models defined by Varady et al. for reverse engineering purposes. Given a 3D surface represented through a dense set of points, we present a novel algorithm that converts to a hierarchical representation . In , the surface is encoded through patches of various shape and size, which form a hierarchical atlas. If belongs to the class of regular models, then captures the most significant features of at all the levels of detail. In this case, we show that can be exploited to interactively select regions of interest on and intuitively re-design the model. Furthermore, intrinsically encodes a hierarchy of useful segmentations of . We present a simple though efficient approach to extract and optimize such segmentations, and we show how they can be used to approximate the input point sets through idealized manifold meshes.
Optical Image Processing Using Light Modulation Displays
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Wetzstein, Gordon; Heidrich, Wolfgang; Luebke, David
We propose to enhance the capabilities of the human visual system by performing optical image processing directly on an observed scene. Unlike previous work which additively superimposes imagery on a scene, or completely replaces scene imagery with a manipulated version, we perform all manipulation through the use of a light modulation display to spatially filter incoming light. We demonstrate a number of perceptually motivated algorithms including contrast enhancement and reduction, object highlighting for preattentive emphasis, colour saturation, de-saturation and de-metamerization, as well as visual enhancement for the colour blind. A camera observing the scene guides the algorithms for on-the-fly processing, enabling dynamic application scenarios such as monocular scopes, eyeglasses and windshields.
Reducing Plenoptic Camera Artifacts
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Georgiev, T.; Lumsdaine, A.
The focused plenoptic camera differs from the traditional plenoptic camera in that its microlenses are focused on the photographed object rather than at infinity. The spatio-angular tradeoffs available with this approach enable rendering of final images that have significantly higher resolution than those from traditional plenoptic cameras. Unfortunately, this approach can result in visible artifacts when basic rendering is used. In this paper, we present two new methods that work together to minimize these artifacts. The first method is based on careful design of the optical system. The second method is computational and based on a new lightfield rendering algorithm that extracts the depth information of a scene directly from the lightfield and then uses that depth information in the final rendering. Experimental results demonstrate the effectiveness of these approaches.
Elastic Tubes: Modeling Elastic Deformation of Hollow Tubes
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Li, H.; Leow, W. K.; Chiu, I.-S.
The Cosserat theory of elastic rods has been used in a wide range of application domains to model and simulate the elastic deformation of thin rods. It is physically accurate and its implementations are efficient for interactive simulation. However, one requirement of using Cosserat rod theory is that the tubular object must have rigid cross-sections that are small compared to its length. This requirement make it difficult for the approach to model elastic deformation of rods with large, non-rigid cross-sections that can change shape during rod deformation, in particular, hollow tubes. Our approach achieves this task using a hybrid model that binds a mesh elastically to a reference Cosserat rod. The mesh represents the surface of the hollow tube while the reference rod models bending, twisting, shearing and stretching of the tube. The cross-sections of the tube may take on any arbitrary shape. The binding is established by a mapping between mesh vertices and the rod s directors. Deformation of the elastic tube is accomplished in two phases. First, the reference rod is deformed according to Cosserat theory. Next, the mesh is deformed using Laplacian deformation according to its mapping to the rod and its surface elastic energy. This hybrid approach allows the tube to deform in a physically correct manner in relation to the bending, twisting, shearing, and stretching of the reference rod. It also allows the surface to deform realistically and efficiently according to surface elastic energy and the shape of the reference rod. In this way, the deformation of elastic hollow tubes with large, non-rigid cross-sections can be simulated accurately and efficiently.
Binary Shading Using Appearance and Geometry
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Buchholz, Bert; Boubekeur, Tamy; DeCarlo, Doug; Alexa, Marc
In the style of binary shading, shape and illumination are depicted using two colours, typically black and white, which form coherent lines and regions in the image. We formulate the problem of assigning colours in the rendered image as an energy minimization, computed using graph cut on the image grid. The terms of this energy come from two sources: appearance (shading) and geometry (depth and curvature). Our contributions are in the use of geometric information in determining colours, and how this information is incorporated into a graph cut approach. This optimization yields boundaries between black and white regions that tend towards being shorter and to run along geometric features like creases. We show a range of results, and demonstrate that this approach produces more coherent images than simpler approaches that make local decisions when assigning colours, or that do not use geometry.
Measuring Complexity in Lagrangian and Eulerian Flow Descriptions
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Jaenicke, H.; Scheuermann, G.
Automatic detection of relevant structures in scientific data sets is still one of the big challenges in visualization. Techniques based on information theory have shown to be a promising direction to automatically highlight interesting subsets of a time-dependent data set. The methods that have been proposed so far, however, were restricted to the Eulerian view. In the Eulerian description of motion, a position fixed in space is observed over time. In fluid dynamics, however, not only the site-specific analysis of the flow is of interest, but also the temporal evolution of particles that are advected through the domain by the flow. This second description of motion is called the Lagrangian perspective. To support these two different frames of reference widely used in CFD research, we extend the notion of local statistical complexity (LSC) to make them applicable to Lagrangian and Eulerian flow descriptions. Thus, coherent structures can be identified by highlighting positions that either feature unusual temporal dynamics at a fixed position or that hold a particle that experiences such dynamics while passing through the position. A new area of application is opened by LagrangianLSC, which can be applied to short pathlines running through each position in the data set, as well as to individual pathlines computed for longer time intervals. Coloring the pathline according to the local complexity helps to detect extraordinary dynamics while the particle passes through the domain. The two techniques are explained and compared using different fluid flow examples.
Geometry-Driven Local Neighbourhood Based Predictors for Dynamic Mesh Compression
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Vasa, Libor; Skala, Vaclav
Surface Reconstruction Based on Hierarchical Floating Radial Basis Functions
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Suessmuth, J.; Meyer, Q.; Greiner, G.
In this paper we address the problem of optimal centre placement for scattered data approximation using radial basis functions (RBFs) by introducing the concept of floating centres. Given an initial least-squares solution, we optimize the positions and the weights of the RBF centres by minimizing a non-linear error function. By optimizing the centre positions, we obtain better approximations with a lower number of centres, which improves the numerical stability of the fitting procedure. We combine the non-linear RBF fitting with a hierarchical domain decomposition technique. This provides a powerful tool for surface reconstruction from oriented point samples. By directly incorporating point normal vectors into the optimization process, we avoid the use of off-surface points which results in less computational overhead and reduces undesired surface artefacts. We demonstrate that the proposed surface reconstruction technique is as robust as recent methods, which compute the indicator function of the solid described by the point samples. In contrast to indicator function based methods, our method computes a global distance field that can directly be used for shape registration.
Accurate Simplification of Multi-Chart Textured Models
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Coll, N.; Paradinas, T.
Scanning and acquisition methods produce highly detailed surface meshes that need multi-chart parameterizations to reduce stretching and distortion. From these complex shape surfaces, high-quality approximations are automatically generated by using surface simplification techniques. Multi-chart textures hinder the quality of the simplification of these techniques for two reasons: either the chart boundaries cannot be simplified leading to a lack of geometric fidelity; or texture distortions and artefacts appear near the simplified boundaries. In this paper, we present an edge-collapse based simplification method that provides an accurate, low-resolution approximation from a multi-chart textured model. For each collapse, the model is reparameterized by local bijective mappings to avoid texture distortions and chart boundary artefacts on the simplified mesh due to the geometry changes. To better apply the appearance attributes and to guarantee geometric fidelity, we drive the simplification process with the quadric error metrics weighted by a local area distortion measure.
Over Two Decades of Integration-Based, Geometric Flow Visualization
(The Eurographics Association and Blackwell Publishing Ltd, 2010) McLoughlin, Tony; Laramee, Robert S.; Peikert, Ronald; Post, Frits H.; Chen, Min
With ever increasing computing power, it is possible to process ever more complex fluid simulations. However, a gap between data set sizes and our ability to visualize them remains. This is especially true for the field of flow visualization, which deals with large, time-dependent, multivariate simulation data sets. In this paper, geometry-based flow visualization techniques form the focus of discussion. Geometric flow visualization methods place discrete objects in the velocity field whose characteristics reflect the underlying properties of the flow. A great amount of progress has been made in this field over the last two decades. However, a number of challenges remain, including placement, speed of computation and perception. In this survey, we review and classify geometric flow visualization literature according to the most important challenges when considering such a visualization, a central theme being the seeding algorithm upon which they are based. This paper details our investigation into these techniques with discussions on their applicability and their relative merits and drawbacks. The result is an up-to-date overview of the current state-of-the-art that highlights both solved and unsolved problems in this rapidly evolving branch of research. It also serves as a concise introduction to the field of flow visualization research.
BqR-Tree: A Data Structure for Flights and Walkthroughs in Urban Scenes with Mobile Elements
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Pina, J.L.; Seron, F.; Cerezo, E.
Poisson-Based Weight Reduction of Animated Meshes
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Landreneau, Eric; Schaefer, Scott
While animation using barycentric coordinates or other automatic weight assignment methods has become a popular method for shape deformation, the global nature of the weights limits their use for real-time applications. We present a method that reduces the number of control points influencing a vertex to a user-specified number such that the deformations created by the reduced weight set resemble that of the original deformation. To do so we show how to set up a Poisson minimization problem to solve for a reduced weight set and illustrate its advantages over other weight reduction methods. Not only does weight reduction lower the amount of storage space necessary to deform these models but also allows GPU acceleration of the resulting deformations. Our experiments show that we can achieve a factor of 100 increase in speed over CPU deformations using the full weight set, which makes real-time deformations of large models possible.
Spectral Mesh Processing
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Zhang, H.; Van Kaick, O.; Dyer, R.
Spectral methods for mesh processing and analysis rely on the eigenvalues, eigenvectors, or eigenspace projections derived from appropriately defined mesh operators to carry out desired tasks. Early work in this area can be traced back to the seminal paper by Taubin in 1995, where spectral analysis of mesh geometry based on a combinatorial Laplacian aids our understanding of the low-pass filtering approach to mesh smoothing. Over the past 15 years, the list of applications in the area of geometry processing which utilize the eigenstructures of a variety of mesh operators in different manners have been growing steadily. Many works presented so far draw parallels from developments in fields such as graph theory, computer vision, machine learning, graph drawing, numerical linear algebra, and high-performance computing. This paper aims to provide a comprehensive survey on the spectral approach, focusing on its power and versatility in solving geometry processing problems and attempting to bridge the gap between relevant research in computer graphics and other fields. Necessary theoretical background is provided. Existing works covered are classified according to different criteria: the operators or eigenstructures employed, application domains, or the dimensionality of the spectral embeddings used. Despite much empirical success, there still remain many open questions pertaining to the spectral approach. These are discussed as we conclude the survey and provide our perspective on possible future research.

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